1. Field of the Invention
The present invention relates to a thin film magnetic head used in recording and reproduction operations for a high density magnetic recording medium.
2. Description of Related Art
A magnetic disk and a magnetic head have been widely used in an information storage unit of a computer system as a magnetic disk unit. The magnetic disk is generally constructed such that the magnetic recording material is deposited on a substrate, for example of material such as aluminum and plastic in a thin film manner by sputtering. Magnetic recording materials include iron, cobalt, nickel or a compound of one of these metals, or they can be of rare earth metals such as neodymium, samarium and gadolinium or a compound of one of the rare earth metals. The magnetic head picks up an electric signal from magnetic fluxes corresponding to data which has been written in a magnetic recording medium, and records an electric signal in the magnetic recording medium in a magnetic flux form. The magnetic head has a non-magnetic ceramic substrate made of alumina (Al.sub.2 O.sub.3) or titanium carbide (TiC), and a circuit element mounted on the non-magnetic substrate for recording and reproduction. The magnetic head is used as close to a magnetic disk surface as possible for increasing the recording density. Although various types of magnetic heads have been recently proposed for increasing of recording density, it is considered to be essential to mount a read head employing a magnetic resistance (MR) element for efficiently reading data recorded by high density recording.
In the MR head a voltage is applied to the MR element for reproduction in principle. Hence, a potential difference is generated between the MR head and the magnetic disk and in the worst case discharging is caused between the MR element and the magnetic disk because of the potential difference so that the MR element and the magnetic disk are damaged.
In order to prevent the damage of the MR element as described above, it is necessary to cover the MR element with a protective film superior in electrical insulation. More particularly, because the voltage of a few volts is applied to the MR element, the electric field of a few MV/cm is generated between the magnetic head and the magnetic disk.
Conventionally, an element of a magnetic head is protected with an Al.sub.2 O.sub.3 film of a few .mu.m in thickness and the Al.sub.2 O.sub.3 film is usually not formed on the sliding surface of the magnetic head. This is the reason why the distance between the magnetic head and the magnetic disk becomes so wide that high density recording is difficult if the sliding surface of the magnetic head is covered with such a thick protective film. In addition, if the Al.sub.2 O.sub.3 protective film is made thin to such an extent that high density recording is possible, there is the problem of the protective film being damaged because the protective film cannot resist the friction between the magnetic head and the magnetic disk because of so called "contact start stop (CSS) cycles".
For coping with this problem, there is a hard carbon film produced by a sputtering method as the protective film indicating high wear resistivity even in a thin film state and it has been used as the magnetic disk protective film. However, as described in, for example, the Proceedings of the International Tribology Conference, 1990, page 1881, the hard carbon film produced by the sputtering method is insufficient for lubricity and wear resistivity so that there is caused another problem that the friction coefficient becomes greater as contact friction is repeated. In practice, in a case where the hard carbon film produced by a sputtering method is used as the magnetic disk protective film, a lubricant coating is necessary. Further, the hard carbon film produced by a sputtering method has a fatal problem in that it is basically electrically conductive. Therefore, with respect to application of the hard carbon film to a magnetic head, because a lubricant cannot be coated in addition to the above problem, the hard carbon film produced by a sputtering method cannot be applied to the magnetic head as is.
In the highly developing information processing field, a technique capable of processing a great capacity of information is required and in conjunction with this high density recording and reproducing technique occupies an important position. For this purpose, it is necessary to make a gap between the MR element and the magnetic disk narrow as described above. More particularly, it is requested that the gap is 1000 .ANG. or less. Thus, it is requested to make the protective film provided on the sliding surface of the MR head as thin as possible. The thickness of the protective film is preferably 300 .ANG. or less, more preferably in a range of 50 to 100 .ANG..
However, there is no protective film produced by a sputtering method that has adequate electrical insulation and wear resistivity with a thickness of about 100 .ANG..
On the other hand, as described in Japanese Patent Application Sho-62-234328, an amorphous hard carbon film produced by a chemical vapor deposition (CVD) method has superior lubricity and wear resistivity even in a thickness of about 100 .ANG.. In addition, the amorphous hard carbon film produced by a CVD method is electrically insulated unlike the hard carbon film produced by a sputtering method, and it is desirable for the MR head protective film.
However, the amorphous hard carbon film has a problem in that adhesion to a ceramic substrate for supporting the magnetic head is not good. This is because the energy of each of the particles coming to the substrate is very small in the CVD method when the film is deposited on the substrate.
In Japanese Unexamined Patent Publication (TokuKaiHei-JP-A-)4-364217, there is disclosed a protective film in which a hydrogen additive amorphous carbon film is adhered to a sliding portion with an adhesion layer. However, the protective film has the structure in which a carbon layer is adhered with the adhesive agent and the thickness of the film is so thick that the high density recording is difficult.
In this manner, in the above conventional technique, there cannot be realized a magnetic head with the protective film having superior characteristics in electrical insulation, wear resistivity, lubricity and adhesion.